Imaging devices are widely used. Commercially, DV cameras are familiar ones. In that keys and electronic circuits are sued to operate the camera so that the images are recorded to a memory through CMOS or CCD sensors.
U.S. Pat. No. 7,102,817, discloses an object lens of holdable microscope. The microscope includes a telescopic elements installed upon a casing. The element includes an inner tube, an outer tube, a guide rod and an object lens. The outer tube is rotatable in a through hole of the casing. By the relative relation of the inner tube, outer tube and the guide rod, the distance between the object lens and an object to be viewed can be changed so as to adjust the focus of the microscope.
However the prior art has the following defects.
The adjusting wheel in the microscope is made of plastic injection which has a large error and is not tolerable to the variation of temperature.
The guide rod is made by two metal bars as a longitudinal guide unit. The inner tube has threads for matching the object lens and thus for rotating and focusing. However the engagement of the inner tube and outer tube are not preferred so that vibrations and deviation occur and thus the image will distort.
The inner tube can not precisely engage to the outer tube and thus idly rotation occurs. As a result, the operation is difficult and not precisely.